Presently, only electronic ballasts are commercially available for T5 fluorescent lamps. This is because conventional passive magnetic ballasts operating at AC mains of 220-240V may not provide enough voltage to sustain the high lamp voltages of T5 lamps with rated powers equal to or higher than 28 W. Electronic ballasts, on the other hand, can provide high ignition voltages using resonant tanks and then provide constant lamp power operation, as well as end-of-life detection and protection functions.
However, electronic ballasts have relatively high power loss and relatively low energy efficiency, especially when used with high-voltage low-current lamps, such as T5 lamps. Existing electronic ballasts also have typical lifetimes of five years and contain toxic/non-biodegradable components.
For countries with 110V mains, the typical practice for controlling high-voltage discharge lamps is to use a step-up transformer to increase the AC voltage for driving the lamps. However, this approach is not only more costly, but also further reduces the energy efficiency of the lighting system. Electronic starters with end-of-life detection functions (e.g. UM2 electronic starters from Tabelek Control System Ltd., UK) have been developed to ignite high-voltage discharge lamps. For 220-240V mains, passive LC (inductive-capacitive) magnetic ballasts have been previously proposed in the lighting industry.
However, LC magnetic ballasts are not available commercially for T5 lamps. One reason is that it is difficult to optimize the values of the inductor and capacitor required for rated power operation of lamps. Also, there is still a misconception that electronic ballasts are always more energy-efficient than magnetic ballasts.
More particularly, there is no magnetic ballast commercially available for high-voltage lamps such as T5 28 W and T5 35 W lamps. T5 28 W lamps have on-state voltages of about 165V at high-frequency operation and about 180V at mains frequency operation. These voltage levels are so close to the 220V-240V AC mains that the voltage difference may not be able to sustain the lamp arc, in view of the vectorial relationships of the AC mains voltage, the voltage drop across the ballast and the lamp voltage.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.